The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is moved by several turbojet engines each housed in a nacelle also accommodating a set of appended actuating devices related to its operation and providing various functions when the turbojet engine is in operation or at shutdown. In particular, these appended actuating devices comprise a mechanical system for actuating thrust reversers.
A nacelle generally presents a tubular structure comprising an air inlet upstream of the turbojet engine, a mid-section intended to surround a fan of the turbojet engine, a downstream section accommodating thrust reversal means and intended to surround the combustion chamber of the turbojet engine, and is generally terminated with an ejection nozzle, the outlet of which is located downstream of the turbojet engine.
Modern nacelles are intended to accommodate a bypass turbojet engine capable of generating via the blades of the rotating fan a hot air flow (also called primary flow) coming from the combustion chamber of the turbojet engine, and a cold air flow (secondary flow) which circulates outside the turbojet engine through an annular passageway, also called flow path. A nacelle for such an engine generally presents an outer structure, called Outer Fixed Structure (OFS), which defines, with a concentric inner structure, called Inner Fixed Structure (IFS), surrounding the downstream compartment of the turbojet engine, which is actually the structure of the engine at the back of the fan, the flow path intended to channel the cold air flow which circulates outside the engine.
The primary and secondary flows are ejected from the engine from the rear of the nacelle. Thus, each propulsion unit of the aircraft is formed by a nacelle and a turbojet engine, and is suspended from a fixed structure of the aircraft, for example under a wing or on the fuselage, via a pylon or a mast fastened to the engine or to the nacelle.
The inner structure of the nacelle is usually formed by two substantially semi-cylindrical half-shells, on either side of the longitudinal vertical plane of symmetry of the nacelle.
The downstream compartment of the turbojet engine, which constitutes the <<core>> area of the turbojet engine, requires periodic maintenance visits.
Indeed, the downstream compartment of the turbojet engine further encloses an accessory gearbox located close to the compressor of the turbojet engine. Typically, this gearbox comprises one or several gear train(s) rotatably driven via the shaft of the compressor on which different accessories are coupled such as for example electrical generators.
The <<core>> area of the turbojet engine also encloses the combustion chamber of the turbojet engine, at the outlet of the compressor, wherein the air/fuel mixture is performed, fuel being introduced in the chamber by a fuel nozzle.
Such equipment should be frequently checked, thereby requiring to have an easy and quick access to the downstream compartment of the turbojet engine.
For this purpose, the half-shells are movably mounted so as to be able to be deployed between a working position where the half-shells form a casing of the downstream compartment of the turbojet engine, and a maintenance position enabling access to the turbojet engine.
In the working position, the half-shells are held in the closed position by means of locks disposed along a junction line located at the lower portion, at <<6 o'clock>>.
According to one solution of the prior art, the half-shells are pivotally mounted about a longitudinal axis forming a hinge at the upper portion of the thrust reverser, at <<12 o'clock>>.
In order to carry out maintenance operations of the turbojet engine, it may be necessary to open the outer structure so as to be able to open the half-shells.
In the case where the outer structure (OFS) is a <<C-duct>>-type structure, that is to say that said structure is constituted by two half-cowls pivotally mounted on hinges positioned at the upper portion of the nacelle, access to the downstream compartment of the turbojet engine is achieved by opening the half-cowls of the outer structure and then opening the half-shells of the inner structure of the nacelle.
When the cowl of the thrust reverser is of the <<D-duct>> type, that is to say, when the half-cowls of the outer structure are connected to the corresponding half-shells of the inner structure by connecting islands, opening the outer structure of the nacelle results in simultaneously opening the inner structure.
In the case of an <<O-duct>>-type outer structure, that is to say when the cowl of the thrust reverser comprises one single annular cowl, extending on either side of an engine pylon to which the nacelle and the turbojet engine are brought back, the aforementioned solution, according to which the half-shells of the inner structure pivot about hinges, is incompatible.
In order to enable opening of the inner structure of the nacelle when the outer structure is fixed or made by an <<O-duct>>-type cowl, there is known a first solution of the prior art, described in the U.S. Pat. No. 4,920,744.
According to this form, access to the downstream compartment of the turbojet engine is provided by a first operation which aims to displace the half-shells downstream of the nacelle, so as to clear the half-shells of the fixed outer structure of the nacelle then by a second operation which aims to drive the half-shells in rotation about an axis parallel to the longitudinal axis of the nacelle, via telescopic connecting rods.
A drawback of this solution is related to the complexity of the mounting and of the opening kinematics, and the time for accessing the areas of the turbojet engine which require frequent maintenance is relatively long.
Another solution described in the French patent application FR 07/01059 and belonging to the Applicant allows overcoming part of the aforementioned drawbacks of the prior art.
The nacelle disclosed by this application comprises an inner structure and an outer structure arranged so as to form a flow channel of the secondary air flow, the inner structure surrounding the turbojet engine and being equipped with means for translational displacement along a rail/slide system substantially parallel to the longitudinal axis of the nacelle, and allowing clearing the downstream compartment of the turbojet engine.
This solution is very advantageous compared to the prior art since it limits the opening kinematics of the inner structure.
Nonetheless, a drawback of this type of structure can for example be identified when the outer cowling of the nacelle is fixed. Indeed, in such a case, translating the inner structure downstream does not allow an easy access to the <<core>> area of the turbojet engine.